You're right. The energy required to accelerate one kg to escape velocity is approximately 18 kilowatt-hours. For that much electricity, you'd typically pay about two dollars (well, maybe 20 in California).
Chemical rockets are very, very inefficient.
I think you left the half out of the equation. I get about half as much. You would also have to add in the potential energy increase. How do you lift the string and counterweight in the first place? Why would you even need a string and counter weight?
Sounds like you want an electric space vehicle with a very long extention cord. Go for it. The rest of us are still stuck on planet earth.